Physical Chemistry

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  • Created by: fjhcab
  • Created on: 04-01-16 10:57
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  • Enthalpy
    • Basics
      • Exothermic gives out heat delta H is NEGATIVE. Bond Making
      • Endothermic takes in heat delta H is POSITIVE. Bond Breaking
      • Combustion is always exothermic
      • q=mc(delta T)
        • q-enthalpy change
        • c-specific heat capacity of water
        • delta T-change in temperature
        • m-mass of water
      • Gradient=change in y/change in x
      • rate of reaction= amount of reactant used or product formed/time
    • Standard enthalpy change of formation
      • Enthalpy change when 1 mole of a compound is formed from its elements in their standard states, under standard conditions
      • Products-Reactants
    • Standard enthalpy change of reaction
      • Enthalpy change when the reaction occurs in molar quantities shown in the chemical equation, under standard conditions
    • Standard enthalpy change of combustion
      • Enthalpy change when 1 mole of substance is completely burned in oxygen, under standard conditions
      • Reactants - Products
    • Standard enthalpy change of neutralisation
      • Enthalpy change when an acids and an alkali react, under standard conditions to form 1 mole of water
    • Reaction Rates
      • Increasing temperature speeds up reactions
        • Particles have more kinetic energy so will move faster colliding more
      • Increasing pressure speeds up reactions
        • At higher pressures particles will be closer together increasing the chance of successful collisions
      • Catalysts can speed up reations
        • Lower activation energy. If activation energy is lower more particles will have enough energy to react
      • Increasing concentration speeds up reactions
        • Particles closer together so will collide more frequently
    • Catalyst
      • Provide an alternative reaction pathway with a lower activation energy
      • Chemically unchanged at the end of the reaction
      • Can be hetero or homo geneous
        • Hetero- Catalyst is in a different phase from the reactant. Increases the surface area of the catalyst increase the amount that can react, increasing the rate of reaction
        • Homo-Catalysts are in the same phase as the reactants. Forms an intermediate species when the reactants combine with the catalyst. which reacts to form the products and reform the catalyst
      • Industry- lower production costs, gives more product in a shorter time & makes better products
        • Less CO2 produced, energy is saved &fossil fuel reserves are preserved
    • Dynamic Equilibrium
      • If position of equilibrium moves to the left more reactants
      • If position of equilibrium moves to the right more products
      • Le Chatelier's Principle
        • If pressure increases equilibrium will shift to the side with fewer gas molecule. If decreased the equilibrium will shift the idea with more gas molecules
        • If concentration of reactants increase equilibrium will shift to the right to make more products. If concentration of products increases equilibrium will shift to the left to make more reactants
        • If there's a change in concentration, pressure or temperature the equilibrium will move to counteract the change
        • If temperature is increase equilibrium will shift to the endothermic direction. If temperature is decreased equilibrium will shift in the exothermic direction
        • Catalyst have NO EFFECT
        • Conditions in industry are a compromise. Lower temperature mean a slower rate of reaction, high pressures are expensive as you need stronger pipes and containers.
    • Equilibrium Constant
      • When you have a homogeneous reaction thats reached equilibrium you can work out a equilibrium constant Kc
        • aA+bB dD+eE
          • Kc=[D]d [E]e/     [A]a [B]b
            • H2+I22HI Kc=[H]2/[H2]1 [I2]1
              • =[H]2/[H2][I2]
                • Substitue in values for H & I


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